Endocrine and metabolic profiles in pregnant and non-pregnant Criollo mares

Abstract

Gestation leads to metabolic changes, prioritizing nutrients’ delivery to the developing fetus (Fowden et al. Equine Veterinary Journal. 1984; 16(4), 239-246). Insulin, adiponectin, and leptin are key metabolic hormones that have been associated with pregnancy success in several species (Coverdale et al. J Anim Sci. 2015; 93(7), 3261-3267.; Meikle et al. Anim. Reprod., v.15, (Suppl.1), p.899-911. 2018). Information on these hormones and their metabolites during gestation of horses is lacking, specifically in native breeds. Therefore, the objective of this study was to establish the endocrine-metabolic profile in pregnant and non-pregnant Criollo mares, a native breed that is popular in South America. Mares (n=56) were categorized as pregnant (n=41) or non-pregnant (n=15). Animals were bled between days 200 and 250 of gestation and the Body Condition Score (BCS) was determined (scale 1-9, Henneke et al. Equine Veterinary Journal. 1983; 15(4), 371-372). The controls were assayed at the same time samples were taken, during the winter, between June and August. Insulin was determined by immunoradiometric analysis, leptin and adiponectin by Radioimmunoassay and other biochemistry variables by spectrophotometer. Hematology variables were determined by hematologic counter. Variables were analyzed by ANOVA using a mixed procedure. The reproductive status did not affect theleptin (9.4±1.6 vs 9.0±1.0 ng/mL, P=0.804 in pregnant and non-pregnant mares respectively), adiponectin concentrations (18.9±2.7 vs 15.5±1.6 ng/mL, P=0.304 in pregnant and non-pregnant mares respectively), nor the BCS (7.3±0.2 vs 7.6±0.1, P=0.356 in pregnant and non-pregnant mares respectively). Insulin (18.2±2.9 vs 17.7±1.7 UI/mL, P=0.644 in pregnant and non-pregnant mares respectively) and glucose (87.0±2.6 vs 83.0±1.6 mg/dL, P=0.180 in pregnant and non-pregnant mares respectively) concentrations were not affected either. Cholesterol concentrations were not affected by the reproductive status, while triglyceride concentrations were higher in pregnant when compared to non-pregnant mares (31.0±1.9 vs 21.6±3.1 mg/dL, P=0.012). Urea and creatinine concentrations were also higher in pregnant than in non-pregnant mares (52.8±1.0 vs 46.7±1.6 mg/dL, P=0.002 and 1.25±0.03 vs 1.01±0.05 mg/dL, P=0.0002 respectively). Hepatic enzymes and white blood cell count were not affected by the reproductive status. This study shows higher concentrations of triglycerides, urea and creatinine in pregnant mares. These changes could be associated with the metabolic prioritization of glucose delivery to the developing fetus, which leads to a differential nutrient partitioning, as reflected in different concentrations of specific metabolites of the protein and lipid pathways.